The present invention relates to subterranean cementing operations, and more particularly, to improved additives comprising low-density particulates, and methods of use.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions often may be used in primary cementing operations whereby pipe strings, such as casings and liners, are cemented in well bores. In performing primary cementing, hydraulic cement compositions may be placed within an annular space between the walls of a well bore and the exterior surface of a pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming therein an annular sheath of hardened substantially impermeable cement that supports and positions the pipe string in the well bore, and that bonds the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Subterranean formations transversed by well bores often may be weak and extensively fractured. In some cases, a formation may be unable to withstand the hydrostatic pressure normally associated with the placement of cement compositions in the formation. In such cases, the hydrostatic pressure may force a cement composition to go undesirably deep into fractures in the formation, which may result in a significant loss of cement composition into the formation during cementing operations. The problem may be referred to as “lost circulation” of the cement composition. This loss of cement composition is problematic because the amount of cement composition that may remain in the annular space may be inadequate to sufficiently bond the exterior surfaces of the pipe string to the walls of the well bore.
Conventional attempts to solve the problem of lost circulation commonly have involved lightening the density of the cement composition, so as, inter alia, to, reduce the hydrostatic pressure to which the formation may be exposed during cementing operations. A traditional means of reducing the density of the cement composition has been to increase the cement composition's water content, because, generally speaking, increasing the concentration of water in a cement composition decreases the cement composition's density. However, this method may be problematic because it may increase the time required for the cement composition to cure, and may result in a cement composition that may lack the desired strength and mechanical properties.
Another alternative means that has been employed to reduce the density of cement compositions has involved the addition to the cement composition of lightweight particulates. Lightweight particulates that conventionally have been used include, inter alia, hollow spheres (e.g., cenospheres, glass hollow spheres, or ceramic hollow spheres). However, the use of conventional hollow spheres has been problematic. Conventional hollow spheres may become poorly dispersed within the cement composition, which may cause the conventional hollow spheres to congregate at shallower depths in the formation, and thus may relegate higher-density portions of the nonhomogenous cement composition to greater depths in the formation, where they may continue to be lost into the formation. Conventionally, great care often must be taken in formulating cement compositions comprising hollow spheres, and in maintaining the viscosity of such cement compositions, so as to prevent the separation and segregation of the conventional hollow spheres, apart from the bulk of the cement composition. This may result in added expense due to, among other things, a need for additional additives and monitoring.